The overarching mission of this Research Core is to understand the relationships that link environmental processes and human health. This requires improved understanding of the relationships of human health with environmental chemicals and with their processes of transport and transformation. Increasingly, however, a broader view of environment-health linkages is now required, one in which genomics and ecology play an increasing role. Future advances will require better understanding of environmental genomics, gene flow, and population dynamics, along with progress in chemical and physical modeling and measurement. Gene flow, for example, can affect the distribution of pathogenicity, the acquisition of antibiotic resistance, or the presence of biodegradative capability in microbial communities. Ecosystem processes govern the nature of coexisting populations at scales from that of microbes to that of continents, with direct effects on humans at all scales. This mission may be thought of as a logical extension of the traditional paradigm in which chemical substances are released to the environment, are subject to fate and transport processes that lead to human exposure, and lead to disease. Our new mission recognizes a new model, in which environmental biota share with chemicals the linkage with human health. The roles of biota are now recognized to include, not only environmental transformation of chemicals, but also synergism between chemicals and microbes, the role of biotically-mediated transport and environmental co-hosts of pathogens, and maintenance of ecosystem functions that enable and govern such processes. In furthering this mission, the Specific Aims of this Core can be expressed as: (1) To foster the development of research projects and programs that address the linkages between ecological processes, exposure to environmental agents, and disease processes in humans. (2) To promote scientific collaboration, both among Environmental Systems and Health Research Core scientists and with members of the other two Research Cores, with the goal of creating new research projects and programs. (3) To promote the development and acquisition of new technologies in the Center Facilities Cores that will facilitate studies in the Environmental Systems and Health Research Core.